Surveillance system with improved detecting network

ABSTRACT

This invention relates to a surveillance system utilizing a telephone line not only for transmitting an alarm signal between an area under surveillance and a central monitoring station but also for supplying the power necessary for the operation of the system. In the operation of one embodiment of this system, electrical signals are generated by a pickup transducer in response to the detection of an intrusion into the area under surveillance, are amplified, and are supplied to a detecting network. After insuring that the signals received are the result of an actual intrusion and not the result of some extraneous noise, the detecting network is operative to trigger an alarm circuit whereby an alarm signal is transmitted via a telephone line to a central monitoring station.

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[72] Inventors David Woodward Reynolds 3,241,069 3/1966 Garfield 328/127X Relay; 3,276,006 9/1966 Hansen 340/261 e Donald George Hang, SilverSpring, both of 3,378,829 4/ 1968 Alafi et a1. 340/416 Md. 3,434, 1643/1969 Forbes 340/258 [21] Appl. No. 861,959 3,461,241 8/1969 Menke179/5 [22] Filed Sept. 29, 1969 r 1 3,487,396 12/1969 Perelman 340/261[45] Patented Oct. 12, 1971 73 Assignee The United States of America as5227" Caldwell man! ExammerPerry Palen represented by the PostmasterGeneral Attorneys-T. Hayward Brown and Joseph A. Hill [54] SURVEILLANCESYSTEM WITH IMPROVED I DETECTING NETWORK ADS'I'RACT: This inventionrelates to a surveillance system 3 Claims, 1 Drawing Fig. utilizing atelephone lme not only for transmitting an alarm signal between an areaunder surveillance and a central mom- U-stoying tation but also fornecessary for 179/5 328/127, 328/171, 340/261 the operation of thesystem. ln tiie operation of one embodi- [51] Int. Cl ..G08b 13/00 memof this System, electrical Signals are generated by a {50] Field ofSearch 340/261, pickup transducer in response to the detection f anintrusion 258 R416; 179/5; 328/127- 171 into the area undersurveillance, are amplified, and are supplied to a detecting network.After insuring that the signals [56] References cued received are theresult of an actual intrusion and not the result UNITED STATES PATENTSof some extraneous noise, the detecting network is operative 3,134,9705/1964 Kelly et al..... 340/261 to trigger an alarm circuit whereby analarm signal is trans- 3,231,823 1/1966 Garfield et a1. 328/127 X mittedvia a telephone line to a central monitoring station.

TO MON lTOR STATION SURVEILLANCE SYSTEM WITH IMPROVED DETECTING NETWORKBACKGROUND OF THE INVENTION ment as much as possible so as to reduce theoverall cost of such a system. 7

One method of surveillance has been to install a radio I bug transmitterwhich picks up audio sounds in the protected area and to have a receivertuned to the transmitter frequency continuously monitored at the centralstation. While sucha system does achieve a desirable feature of notmaking an intruder aware of the fact that he has been detected, such asystem may be undesirable since it may require the continuous monitoringof the receiver at the central station. Furthermore, such a system maybe limited by relevant communications laws, as for example by the numberor range of frequencies available for such operations.

Still other methods of surveillance, while utilizing a telephone linefor the transmission of an alarm signal, merely use the lines for thatpurpose, thus requiring a separate source of electrical power for theoperation of the system.

The surveillance system of this invention is especially adapted for useon the type of telephone line commonly referred to as a private line.That is, a telephone line of the type in which the mere picking up ofthe receiver at one end automatically causes the ringing of a telephoneat the opposite end. Such systems are well known and are commonly foundin such places as airports, hotels, and the like.

Accordingly, one object of this invention is to provide improved meansfor maintaining the continuous surveillance over an area to be protectedwhich does not require continu' ous monitoring by an operator at acentral station.

Another object of this invention is to provide an improved surveillancesystem which permits the detection of an intrusion into an area beingprotected without making the intruder aware that he has been detected.

Still another object of this invention is to provide an improvedsurveillance system which utilizes a telephone line as a means formaintaining surveillance over an area to be protected.

Still another object of this invention is to provide an improvedsurveillance system which utilizes a telephone line not only in thetransmission of an alarm signal to a central monitoring station but alsoas a source of power for the operation of the system. 7

SUMMARY OF THE lNVENTlON ln a preferred embodiment of the continuoussurveillance system of this invention, an acoustical transducer is usedto detect the presence of an intrusion into an area being protected.Electric signals are generated by the transducer in response to soundsgenerated in an area to be protected and are supplied to an amplifyingcircuit. The output from the amplifier circuit is supplied to adetecting network which controls the application of an alarm circuitonto a private telephone line. The detecting network includes anintegrating and limiting circuit for insuring that the signals receivedfrom the trans- BRlEF DESCRIPTION or THE DRAWING The sole FIGURE is aschematic diagram of the circuit of a preferred embodiment of thisinvention.

,DESCRIPTlON OF THE PREFERRED EMBODIMENT Referring now to the drawing,there is shown a schematic diagram in which lines b-] and L-2 arerespectively the power leads froma "private" telephone line. These linesprovide all of the electrical power necessary for the operation of thesystem of this invention. A capacitor C-8 is connected between the leadsand acts as a RF bypass to prevent stray RF (from nearby radiotransmitters or the like) from causing a false alarm. The telephone lineL-l is connected to one side of a stabilizing capacitor C4 through azener diode D-2 and a resistor R-23. The telephone line L-2 is connectedto the other side of capacitor C-l through an "on-oft" switch 8-1. Thezener diode D-2 drops the basic 48 volt DC telephone voltage to 24volts. However, if the telephone line is a 24 volt line, then the zenerdiode D-23 should instead be jumpered out. Thus, as shown in thedrawing, L-l is the positive line while L-2 is the negative" line. Thepresence of the resistor R-Z provides a time delay RC circuit with C-lto permit a person to activate the network, as by closing the on-oft"switch 5-! and still have time to leave the room without setting off thealarm by any noise in his leaving. Furthermore, this same RC networkacts as a power-supply filter to prevent extraneous telephone linenoises from setting off the alarm.

Transducer means are provided for generating or producing electricalsignals in response to the detection of an intrusion into the area beingkept under surveillance. in this instance, it is desired to utilize atransducer which is sensitive to certain noises from an intrusion orintruder, such as the hissing of an acetylene torch or sharp sounds froma tool, to activate the alarm. Thus, an acoustical transducer means M isutilized and may comprise a microphone with uitably designed frequencyresponse. However, it is not the intention of this invention to belimited to such a transducer and any suitable transducer may beutilized. As is shown in the FIGURE, one side of the microphone M isconnected to the negative line L-2 and the other side is connectedthrough a DC blocking capacitor C-2 to the input of the amplifyingmeans.

Means are provided for amplifying the signals generated by themicrophone M as a result of the detection of an intrusion. In thisinstance, the means comprises a multistage transistor amplifierutilizing NPN transistors. Specifically, transistor 0-1 is included inthe first stage of the amplifier and has a biasing resistor R-lconnected between its collector and its base, a load resistor R-2connected between its collector and the positive line L-l, an' inputresistor R-3 connected between its base and its negative line L-2, and adegeneration resistor R-4 connected between its emitter and the negativeline L-Z. Under normal standby operating conditions, transistor 0-! willbe biased to a nearly nonconducting state. However, when an intrusion isdetected, the signal supplied by the microphone M through the blockingcapacitor C-2 to the base of transistor 04 will cause the transistor toconduct and produce a signal at its collector, this signal beingsupplied to the next stage of the amplifier.

The second stage of the amplifier is similar, if not identical, to thefirst stage and includes transistor ()4 having a biasing resistor R-5connected between its collector and its base, a load resistor R-6connected between its collector and the positive line L-l, an inputresistor R-7 connected between its base and the negative line L-Z, and adegeneration resistor R-8 connected between its emitter and the negativeline L-2. A DC blocking capacitor (3-3 is connected between thecollector of transistor Q-l and the base of transistor 0-2 and is usedto couple the first stage of the amplifier to the second from thecollector of transistor -2 and supplied to the third stage oftheamplifier.

The third stage of the amplifier again is similar, if not identical, tothe first two stages. Transistor 0-3 has a biasing resistor R-9connected between its collector and its base, an input resistor R-llconnected between its base and the negative line l..-2, a load resistorR-10 connected between its collector and the positive line L-l, and adegeneration resistor R-l2 connected between its emitter and thenegative line L-2. The third stage of the amplifier is also capacitivelycoupled to the second stage by means of a DC blocking capacitor C-4which is connected between the collector of transistor 0-2 and the baseof transistor 0-3.

The output of the amplifier is supplied to an alarm means which isresponsive to generate an alarm signal which is to be transmitted alongthe telephone line L-l and L-2 back to a monitoring station. However,since random or external noise, such as from thunder or from the honkingof the horn of a passing car, may activate the system, it is highlydesirous to provide means within the system for preventing the alarmmeans from responding until a time interval has passed sufficient toinsure that signals being received from the transducer are in responseto an actual intrusion into the area being protected and not a falsealarm.

Accordingly, the means for preventing an immediate 4 response of thealarm means includes an integration means and a switch means. Theintegration means provides a time delay which permits actuation of thealarm means only after a predetermined level of output from thetransducer is reached, thus preventing actuation of the alarm from afalse alarm source. The switch means is responsive to the integrationmeans to apply the alarm means to the telephone line only after apredetermined level of output from the transducer is reached. In thepreferred embodiment, the integration means includes a detectortransistor 0-4 which is capacitively coupled to the output of theamplifier via a capacitor C-5 connected between the collector oftransistor Q-3 and the base of transistor 0-4. An input resistor R-14 isconnected between the base of transistor 04 and the negative to line L-2with the emitter of transistor 0-4 being connected to the negative lineL-Z through a field-effect current regulator diode D-3 and a voltagedividing and control network. Diode D-3 may be selected, for example,from the family of current limiter diodes having type numbers lN5283through 1N53 l4 manufactured by Motorola Semiconductors. The voltagedividing and control network has two branches, one branch includingseries connected resistors R-17 and R-22 with the other branch includinga diode D-l-connectedin shunt with a resistor R-l6, this circuit beingserially connected to the negative line L-2 through an integratingcapacitor 0-7.

The junction of resistors R-17 and R-22 is connected to the I Isufficient current passes through resistors R-17 and R 22, the

silicon controlled rectifier SCR-1 is "triggered" into its conductingstate to connecting the alarm means across the telephone line.

In the operation of the preventing means, the output of the amplifier issupplied to the detecting transistor Q-4 causing the transistor toconduct. Thus, positive pulses appear at the emitter of the transistor,and current is supplied through diode D-3 and diode D-l to charge theintegrating capacitor C-7. Diode D-3 is a current-limiting type diodewhich increases its forward resistance to prohibit current fromexceeding a certain value and may be characterized as the electricaldual of the Zener diode. Diode D-3 thus prevents one extremelyloud soundfrom setting off the alarm, requiring, rather, that several sounds bepresent. Because of the low forward impedance of the diode D-l, resistorR-16 is effectively shunted. As the capacitor C-7 charges, the impedancelooking into the diode D] rises diverting most of the current into thebranch containing resistors R-17 and R-22. When the current level inthis branch reaches a predetermined level, the silicon controlledrectifier SCR-l will be triggered" into i t s conducting state to applythe alarm means directly across telephone lines L-l and L-Z.

Note that resistor R-17 is necessary in order to overcome the effect ofthe forward voltage drop in the diode D-l.

' Without resistor R-l7 there would be little or no integration actionsince the amount of forward voltage developed across the diode wouldtend to immediately trigger the silicon controlled rectifier SCR-lbefore the capacitor C-7 was charged,

the result being that upon the detection of any sound by the transducerM, the alarm means would be applied to the telephone lines. ResistorR-l6 provides a controlled leak-off time for the charge on capacitorC-7, and provides controlled memory time for past sounds.

The alarm means comprises a unijunction oscillator circuit having atiming branch including a resistor R-20 connected in series with acapacitor C-6, the junction of these two elements being connected to theemitter electrode of a unijunction transistor 0-5. Base 2 of theunijunction transistor 0-5 is connected to the other side of resistorR-20 and to telephone line L-l while base 1 of the unijunctiontransistor Q5 is connected through a load resistor R-Zl to the otherside of the capacitor C-6 and to telephone line L-2 through the siliconcontrolled rectifier SCR-l. A relatively low resistance R-l9 isconnected in shunt across the unijunction oscillator circuit.

In the operation of the alarm means, the triggering of the siliconcontrolled rectifier SCR-immediately places the low resistance R-l9directly across the telephone line and causes a relatively large flow ofDC current through the line. This in turn initiates ringing of thetelephone at the monitoring station which may be a police station orother suitable area. The unijunction oscillator circuit, the specificoperation of which is well known in the art and which will not bedescribed in any detail herein, is also activated by the telephone linevoltage and will modulate the telephone line with a single continuoustone. Thus, an operator at the monitoring station answering the phonewill hear the modulated signal and at once recog nize that an intrusionhas occurred in the area being protected.

If desired, a telephone jack .l-l can also be connected across theunijunction oscillator circuit and utilized to provide an additionalalarm device. For instance, an audible alarm mechanism similar to abuzzer could be installed. Or, an external carbon microphone, or atransistor amplifier with a magnetic microphone might be plugged intothe jack to permit an audio monitoring of the area. The jack may also beused with an audible alarm to test the operation of the unit prior toits installation.

It generally will not be desirous to have the surveillance meanscontinuously connected to a telephone line. Further, it

generally will be highly desirous to provide means for resetting thesystem, that is, where the capacitors C-1 and C-7 are completelydischarged. Thus, means are provided for restoring the network to itsoriginal condition and for disconnecting the system from the line.Specifically, a double pole, double throw switch 8-] is utilized forboth of these functions, one of the poles being used to control theconnection of a discharge resistor R-18 to capacitor C-7 and the secondpole being used to provide means for connecting another dischargeresistor Rl3 across capacitor C-l. In the oft position of the switch 5-the resistor R-18 is connected directly across the capacitor C-7 toprovide a means for dissipating any charge on the capacitor. Similarly,the resistor R-13 will be connected directly across the capacitor 0-1 toprovide a means for dissipating any charge thereon. However, with theswitch 5-1 in the on position, resistors R-13 and R48 will not beconnected in the system and line voltage will be supplied to the system.

While we have shown and described only a particular embodiment ofthisinvention, it will be obvious to those skilled in it without departingfrom its broader aspects. Therefore, it is the intention of the appendedclaims to cover all changes and modifications as fall within the truespirit and scope of this invention.

What we claim as new and novel and desire to secure by Letters Patent ofthe United States is:

1. An electronic surveillance means comprising:

a. Acoustical transducer means for converting sound energy intoelectrical signals;

b. Transistor means for amplifying said electrical signals;

c. Alarm means responsive to said amplified signals for indicating at amonitoring station an intrusion, said alarm means including;

1. a unijunction oscillator circuit,

2. a resistor connected in electrical shunt with said unijunctionoscillator circuit, and

3. means for connecting said unijunction oscillator circuit and saidresistor to a telephone line;

d. Means for preventing said alarm means from responding to saidamplified signals until a predetermined time interval has passedsufficient to insure that said electrical signals from said transducermeans is in response to an actual intrusion, said preventing meansincluding;

1. solid state switching means for selectively connecting said alarmmeans to the telephone line,

the art that various changes and modifications may be made to I 2.integration means for controlling the operation of said solid stateswitching means, and 3. limiting means for limiting the current to saidintegration means thereby insuring that a sufficient number of soundsare present from an intrusion before said alarni means is activated. 2.An electronic surveiilance means as described in claim 1 wherein:

a. Said solid state switching means comprises a silicon controlledrectifier having a trigger electrode; and b. Said integration meanscomprises a capacitive network connected to the output of saidamplifying means, a said capacitive network being coupled to saidtrigger electrode and controlling the conducting state of said siliconcontrolled rectifier, said silicon controlled rectifier operable toconnect said unijunction oscillator circuit and said 7 resistor to atelephone line. 3. An electronic surveillance means as described inclaim 2, further including:

a. Resistor means for dissipating any charge on said capacitive means torestore it to an uncharged condition, and b. Switch means operable toconnect said resistor means directly across said capacitive means fordissipating any charge thereon.

1. An electronic surveillance means comprising: a. Acoustical transducermeans for converting sound energy into electrical signals; b. Transistormeans for amplifying said electrical signals; c. Alarm means responsiveto said amplified signals for indicating at a monitoring station anintrusion, said alarm means including;
 1. a unijunction oscillatorcircuit,
 2. a resistor connected in electrical shunt with saidunijunction oscillator circuit, and
 3. means for connecting saidunijunction oscillator circuit and said resistor to a telePhone line; d.Means for preventing said alarm means from responding to said amplifiedsignals until a predetermined time interval has passed sufficient toinsure that said electrical signals from said transducer means is inresponse to an actual intrusion, said preventing means including; 1.solid state switching means for selectively connecting said alarm meansto the telephone line,
 2. integration means for controlling theoperation of said solid state switching means, and
 3. limiting means forlimiting the current to said integration means thereby insuring that asufficient number of sounds are present from an intrusion before saidalarm means is activated.
 2. a resistor connected in electrical shuntwith said unijunction oscillator circuit, and
 2. integration means forcontrolling the operation of said solid state switching means, and
 2. Anelectronic surveillance means as described in claim 1 wherein: a. Saidsolid state switching means comprises a silicon controlled rectifierhaving a trigger electrode; and b. Said integration means comprises acapacitive network connected to the output of said amplifying means, asaid capacitive network being coupled to said trigger electrode andcontrolling the conducting state of said silicon controlled rectifier,said silicon controlled rectifier operable to connect said unijunctionoscillator circuit and said resistor to a telephone line.
 3. Anelectronic surveillance means as described in claim 2, furtherincluding: a. Resistor means for dissipating any charge on saidcapacitive means to restore it to an uncharged condition, and b. Switchmeans operable to connect said resistor means directly across saidcapacitive means for dissipating any charge thereon.
 3. limiting meansfor limiting the current to said integration means thereby insuring thata sufficient number of sounds are present from an intrusion before saidalarm means is activated.
 3. means for connecting said unijunctionoscillator circuit and said resistor to a telePhone line; d. Means forpreventing said alarm means from responding to said amplified signalsuntil a predetermined time interval has passed sufficient to insure thatsaid electrical signals from said transducer means is in response to anactual intrusion, said preventing means including;